Distinctive signals of boosted dark matter from its semi-annihilation

Dark matter can be boosted by various mechanisms, which may produce characteristic signals that are different from those of canonical dark matter. We show that the semi-annihilation $\chi\chi\to\bar{\chi}\nu$ produces signals that are distinctive from those of other semi-annihilation and standard dark matter annihilation processes. Because the boosted dark matter produced by the semi-annihilation process is regarded as a high-energy neutrino, the total flux of the dark matter and the accompanying neutrino produce double peaks in the energy close to the dark matter mass. We show that it will be possible to detect both of the particles produced at the Sun using future large volume neutrino detectors such as those of the Deep Underground Neutrino Experiment and Hyper-Kamiokande.